Cold-seep macrofaunal assemblages in cores from Vestnesa Ridge, eastern Fram Strait, during the past 45000 years

Abstract

Four cores from 1200 m water depth from Vestnesa Ridge on the western Svalbard margin in the eastern Fram Strait were studied for their content of fossil macro-faunas. Three of the cores were collected from a pockmark with active methane seepage, and one core (control core) was taken just outside the seepage area for comparison. Together the cores cover the last 45 000 years (mid-late Weichselian glacial, the deglaciation and the Holocene). The records show a range of influence of methane from no seepage (control core) and, although variable through time, from moderate seepage, to strong and very strong seepage. All cores have been analysed for the macrofossils >1 mm, trace fossils, planktic foraminifera, stableisotopes, geochemistry and sedimentology. The main purpose of the study is to improve our knowledge of the fossil macrofauna and past environmental changes related to the impact of methane emissions in the area. The core recovered outside the pockmark contained no fossil macrofaunas, while cores from inside the pock-mark contained chemosymbiotic bivalves, and in some cases a rich macrofauna. The faunal relationships with the sedimentary environments confirm a close con-nection between the macrofauna and the variability in influence of cold seepage, particularly seen in the occurrence of chemosymbiotic bivalves <i>Archivesica arctica, Isorropodon nyeggaensis</i>, potentially chemosymbiotic bivalve <i>Rhacothyas kolgae</i>, polychaetes. A barren zone in the core that was taken from the deepest part of the pockmark may indicate that a blow-out took place in the late glacial and the deglaciation into the early Holocene at c. 21,000–9000 years.